Heparin-Affinity of human extracellular-superoxide dismutase in the brain

Extracellular-superoxide dismutase (EC-SOD) is one of the three SOD isozymes in humans and has affinity for heparin-like sulfated glycosaminoglycans in the extracellular matrix. The C-terminal portion of EC-SOD is responsible for the heparin-affinity of this enzyme, but this portion should be a target of proteinases. Recently, Oury et al. reported that EC-SOD is localized within the cytoplasm of neuronal cells, while this enzyme is found in the extracellular matrix in most other tissues. It has been speculated that the heparin-binding domain of EC-SOD in the brain is sensitive to proteolysis, which may result in a loss of extracellular immunoreactivity. This study was performed to investigate the heparin-affinity of EC-SOD in the human brain. We found that human EC-SOD in brain tissue has high heparin-affinity similar to that in the umbilical cord. Moreover, heparin-affinity of EC-SOD in brain homogenate was not decreased by incubation at 37 degrees C for 72 h. The proteolytic activity in brain homogenate might be less than that in umbilical cord homogenates. The intracellular localization of EC-SOD could contribute to its slow clearance from the brain and maintenance of its physiological functions in the brain.